Conventionally, there has been proposed an organic EL element that has a configuration as shown in FIG. 6 (see Japanese Patent Application Laid-Open No. 2006-331694). In this organic EL element, one electrode (a cathode) 11 is laminated on a surface of a substrate 14, and an emission layer 13 is laminated on a surface of the electrode 11 while inserting an electron-injection/transport layer 15 therebetween, and the other electrode (an anode) 12 is laminated on the emission layer 13 while inserting a hole-injection/transport layer 16 therebetween. Then, the organic EL element is further provided at the above-mentioned surface side of the substrate 14 with a sealing member 17. Accordingly, in the organic EL element, light emitted by the emission layer 13 is radiated through the electrode 12 formed as a transparent electrode and the sealing member 17 formed of a transparent body.
Examples of materials for the electrode 11 having reflectivity include Al, Zr, Ti, Y, Sc, Ag, In, and the like. Then, examples of materials for the electrode 12 being an optically-transparent electrode include Indium-Tin Oxide (ITO), Indium-Zinc Oxide (IZO) and the like.
Generally, light extraction efficiency for an organic EL element is about 20% to 30%. Therefore, in the field of the organic EL element, it is desired that external quantum efficiency is improved for top-emission and bottom-emission types of any organic EL elements. Similarly, for the organic EL element having the configuration as shown in FIG. 6, it is desired that the light extraction efficiency is improved.